Attachment arm



FIG. 1 is a perspective view showing the new design for an attachment arm;

FIG. 2 is a side view thereof;

FIG. 3 is a side view thereof;

FIG. 4 is a front view thereof;

FIG. 5 is a rear view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken line showing of the helmet and hearing protector is included for the purpose of illustrating environmental use only and forms no part of the claimed design. 

CLAIM The ornamental design for an attachment arm, as shown and described. 